a) Field of the Invention
The present invention is directed to a device for indexing magazine compartments and wafer-shaped objects contained therein, particularly semiconductor wafers and templates, the magazine being adjustable vertically in a measurable manner relative to a handling plane for removal and charging by a magazine seat of a wafer handling device by means of a magazine lift for the purpose of processing such wafer-shaped objects. Such technical solutions can be applied in the manufacture of integrated circuits, particularly for handling operations, and are known, for example, from U.S. Pat. No. 4,895,486.
b) Description of the Related Art
In the manufacture of integrated circuits, semiconductor wafers must be transported between different processing stages to individual processing machinery. It is increasingly common for such transport to be effected in standardized transport containers, so-called standard mechanical interface boxes (SMIF boxes), the magazine within whose compartments the semiconductor wafers are located being fastened in a suitable manner to the base of these transport containers. For the purpose of charging the processing machines, the magazines are unloaded from the transport containers by suitable devices and the semiconductor wafers are removed by a removing and charging device. After processing, the semiconductor wafers are returned to the compartments of the magazine and the magazine is returned to the transport containers.
The possible use of impact pressure sensors or reflex couplers which detect the semiconductor wafers in the magazine has the disadvantage that the magazine must be serviced in a determined sequence. In so doing, the semiconductor wafers may not be removed from the magazine in arbitrary sequence; rather, the charging magazine must be emptied starting from the bottom and proceeding upward and the dispensing magazine must be filled starting from the top and proceeding downward because of the required sensor arrangement and the removal and charging of semiconductor wafers dictated thereby. Consequently, a fixed allocation of the wafer to a determined level is not adhered to. Such technical solutions cannot be applied for inspecting conventional random samples or for use in the above-mentioned transport containers.
It is known from U.S. Pat. No. 4,895,486 to determine the presence of wafer-like objects in a carrier (magazine) and their position relative to a reference plane in the carrier by means of a monitoring device in that a first signal reporting the presence of such an object is combined with a position signal for the object. The first signal is obtained by an optoelectronic sensor which monitors the space in which the objects can be located. The second signal is formed via a position encoder coupled with a drive for moving the carrier up and down.
To determine the reference plane and possible location of the objects, the carrier space is divided vertically into segments. In addition to a segment serving as reference plane and segments without wafer-like objects, window segments in which objects may be present are also defined. An indexing of the carrier is effected in that, after the reference plane in the carrier is detected by measuring techniques, the locations of the window segments are determined by computer based on construction data of the respective carrier being used and are stored in the computer.
Although the quantity of objects and their locations relative to a reference plane within the carrier can be determined by means of the described solution, the carrier or the removing and charging device must be positioned according to the grid dimensions of the compartments of the carrier in order to remove the objects from the carrier. If divergent carrier geometries and tolerances are not allowed for in so doing, errors cannot be ruled out. In particular, problems arise in optional charging of empty carriers.
Further, it is possible to monitor the correct position of the object in the carrier by means of an additional optoelectronic sensor when the carrier is being transported upward in the vertical direction. In this way, objects protruding from the carrier as the result of faulty or incorrect handling are protected against damage when being returned to the transport containers. If an object protruding from the carrier is detected, the transport of the magazine is stopped and manual intervention on the part of the operator is required to correct the error.
While the detection of protruding objects has practical importance, the required manual intervention causes unnecessary delays in continued processing by interfering with the sterile conditions and possibly the climatic conditions of the processing machines within the machine enclosure. This can result in failure of the machine.
Therefore, the problem to be solved consists in ensuring that the removing and charging device can precisely access any given and predetermined plane of the magazine independent of dimensional tolerances so as to avoid the costs involved in extra adjustments and to provide for a more flexible use of the described transport containers. Moreover, it must be ensured that operation may be resumed immediately when detecting incorrectly positioned semiconductor wafers.